Weighing scale

ABSTRACT

A strain plate ( 4 ) is placed on a base plate member ( 3 ) without using any fixing means. The strain plate ( 4 ) is formed with a straight groove ( 7 ) for restricting its strain direction to one direction. The base plate member ( 3 ) is fitted with position regulating members ( 14 ) opposite the four corner portions of the strain plate ( 4 ), individually. Each position regulating member ( 14 ) is formed with a slit such that a part of it can be elastically deformed with ease. The position regulating blocks can absorb the displacement of the sides of the strain plate that is caused when the strain plate ( 4 ) is deformed as a weighing machine ( 1 ) is loaded.

TECHNICAL FIELD

The present invention relates to a weighing machine for weighing humanbodies and the like.

BACKGROUND ART

In a conventional weighing machine, a strain plate is strained in amanner such that a load from a scale plate on which an object to beweighed, such as a human body, is placed is transmitted to andconcentrated on one point by means of a load transmission mechanism(beam balance) that is formed of a plurality of metal plates combinedwith one another. The change of a resistance value of a strain gaugethat is pasted on the strain plate is detected, or the change ofcapacitance is detected by varying the distance between two electrodeplates as the strain plate is displaced, and the change is convertedinto load.

In the beam balance described above, metal plates are used incombination with one another in a manner such that they are set uprightto stand load from the scale plate, and load transmitting metal platesfor transmitting the load from the scale plate to a beam metal platemust be constructed as knife edge fittings, so that the balance normallyinevitably has a great thickness of 35 mm or more. Further, knife edgeportions are subjected to a very high pressure, so that they are forcedto deform and wear away after repeated use, thus failing to ensurelong-term reliability.

To cope with this, a technique of a thin weighing machine with simpleconstruction and high long-term reliability is described in PublicationNo. WO00/06977, for example. An outline of this weighing machine willnow be described with reference to FIGS. 13 and 14.

As shown in FIG. 13, a weighing machine 50 is formed in a manner suchthat a scale plate 51, one strain plate 52, and a base plate 53 arecombined in layers. The strain plate 52 and the scale plate 51 are fixedin layers with scale plate spacers 54 between them by means of bolts andscrews, and the strain plate 52 and the base plate 53 are fixed inlayers with base plate spacers 55 between them by means of bolts andscrews. The base plate 53 is provided with a circuit portion 56, whichincludes control and arithmetic circuits such as a microcomputer, adisplay portion 57 for displaying the result of computation, and a powersource retaining portion 58, and its plane shape is optional.

Further, the scale plate 51 in the form of a plate is connected to loadreceiving portions 59 of the strain plate 52 by means of the scale platespacers 54. The weighing machine 50 is configured to be a weighingmachine that is formed of three flat plates and can be made very thin.

In the case where the weighing machine 50 is placed on a floor surface,leg portions 60 can be provided on a part of the strain plate 52. Forexample, one or more leg portions 60 provided on the strain plate 52 canbe arranged in any other region(s) of outer frames 61 than regions rightunder fixing portions 62 to which the base plate 53 is fixed. To attainthis, hollow portions 63 are formed in the base plate 53.

The strain plate 52 is formed integrally of a sensitive portion 66including a strain gauge 65 for use as sensing means, load transmittingbeams 64 connecting with the sensitive portion 66, and load receivingportions 59. An upper surface 67 of the one strain plate 52 is providedwith a center groove portion 68, which includes the sensitive portion 66and is formed extending parallel to a straight line L—L that connectsthe respective center points C of the load receiving portions 59. Aweight applied to the scale plate 51 is received dispersedly by means ofthe load receiving portions 59, the load is caused to act concentratedlyon the sensitive portion 66 by means of the load transmitting beams 64,and strain or deformation of the sensitive portion 66 is picked up as achange of the quantity of electricity by means of the strain gauge 65.

The load applied to the weighing machine 50 of FIG. 13 acts on thestrain plate 52. In a weighing machine such as a scale that measures aheavy weight, in particular, screw portions for fixing the strain plate52 and the base plate 53 are liable to loosened by repeated loading. Ifthe screw portions loosen, the position of the strain plate 52 relativeto the base plate member is shifted, so that the way the strain plate 52is strained changes with every measurement. In consequence, measurementsof the same weight involve different ways of transmission to the straingauge 65, inevitably causing measurement errors. Further, a shock of afall or the like also creates gaps between the strain plate 52 andscrews, so that the measurement accuracy lacks in reliability.

Another prior art is also described in Publication No. WO00/06977. Inthis case, a strain plate and a base plate are fixed by means of thefollowing arrangement instead of screwing. As shown in FIG. 14, a baseplate 53 is in the form of an open-topped box, a strain plate 52 isarranged in the box, and fixing members 70 for preventing vibration anddisplacement of the strain plate 52 are arranged between the cornerportions of the strain plate 52 and a peripheral wall 69 of the baseplate 53.

If sides 70 a of the fixing members 70 and sides 52 a of the strainplate 52 are brought intimately into contact with one another, in aweighing machine of the alternative prior art described above, however,the central portion of the strain plate 52 sinks during measurement, andthe sides 52 a of the strain plate 52 warp, thereby pressing the innersides 70 a of the fixing members 70. After repeated use, therefore, gapsare formed between the fixing members 70 and the strain plate 52, sothat the strain plate 52 is dislocated, and the measurement may possiblybe subject to dispersion, as in the case of the aforesaid screwingmethod. If gaps are previously provided between the fixing members 70and the strain plate 52 to prevent this, however, the position of thestrain plate 52 is finely shifted with every measurement, so thatmeasurement errors may possibly occur. A shock of a fall or the likealso creates gaps between the fixing members 70 and the strain plate 52,resulting in the same problem.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a thin weighingmachine of high-reliability, which stands repeated use and whosemeasurement accuracy is influenced little by a shock of a fall or thelike.

In order to achieve the above object, a weighing machine according to anaspect of the present invention comprises a substantially flat strainplate adapted to be deformed when loaded, a sensor for detectingdeformation of the strain plate, a base plate member carrying the strainplate thereon, and a scale plate member located on the upper surface ofthe strain plate and capable of transmitting load to the strain plate,the sides of the strain plate being held by means of elastic positionregulating members, individually.

The weighing machine according to this aspect can adopt the followingforms.

The strain plate has a strain-direction regulating portion forregulating the direction of a strain produced in the strain plate as thestrain plate is deformed. The sensor is a strain gauge attached to thestrain plate corresponding to the strain direction of the strain plate.The position regulating members hold at least the sides of the strainplate which extend at right angles to the strain direction.

The strain plate is formed with at least two sides extending at rightangles to the strain direction and opposed to each other across thestrain-direction regulating portion, the two sides being held by meansof the position regulating members, individually. Further, the positionregulating members hold a plurality of portions of the sides of thestrain plate perpendicular to the strain direction. Furthermore, theposition regulating members hold two portions near the opposite endportions of the sides of the strain plate perpendicular to the straindirection.

The position regulating members hold those sides of the strain platewhich extend parallel to the strain direction as well as the sides ofthe strain plate perpendicular to the strain direction. The strain plateis formed with a plurality of sides parallel to the strain direction,the sides being held by means of the position regulating members. Theposition regulating members for holding the sides parallel to the straindirection hold portions near the end portions of the sides of the strainplate parallel to the strain direction.

The strain plate is formed with at least two sides extending at rightangles to the strain direction and opposed to each other across thestrain-direction regulating portion, and the position regulating membersfor holding the sides perpendicular to the strain direction hold oneportion near the center of each side perpendicular to the straindirection.

Each of the position regulating members includes a fixed portion fixedto the base plate member and a contact portion formed integrally withthe fixed portion and in contact with the side of the strain plate, thecontact portion being made elastic by means of a slit formed between thecontact portion and the fixed portion.

Each of the position regulating members is composed of a fixed portionfixed to the base plate member and an elastic portion in contact withthe side of the strain plate and attached to the fixed portion.

The strain plate has two openings in symmetrical positions on theopposite sides of the strain gauge, the position regulating membersholding inner walls formed in the openings.

Each of the position regulating members has a protuberance, theprotuberance being in contact with the side of the strain plate.

The individual sides of the strain plate are arranged so as to be incontact with the position regulating members only.

The plane shape of the strain plate is substantially rectangular, andthe position regulating members are substantially L-shaped membersarranged individually near the four corners of the rectangular shape.The substantially L-shaped member is formed with a hole portion suchthat the L-shaped member can be fixed to the scale plate member with thehole portion fitted on a fitting member protruding substantiallyperpendicularly from the scale plate member.

The position regulating members for holding the sides of the strainplate perpendicular to the strain direction and the position regulatingmembers for holding the sides of the strain plate parallel to the straindirection are formed separately from one another.

Further, a weighing machine according to another aspect of the presentinvention comprises a substantially flat strain plate adapted to bedeformed when loaded, a sensor for detecting deformation of the strainplate, a base plate member carrying the strain plate thereon, and ascale plate member located on the upper surface of the strain plate andcapable of transmitting load to the strain plate, the position of thestrain plate in the planar direction being settled by means of elasticposition regulating members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a weighing machine according to a firstembodiment of the present invention, the weighing machine being clearedof its scale plate;

FIG. 2 is a sectional view taken along line A—A of FIG. 1;

FIG. 3 is a plan view of the weighing machine (fitted with the scaleplate) of FIG. 1;

FIG. 4A is a plan view of a position regulating member of FIG. 1;

FIG. 4B is a right-hand side view of the position regulating member ofFIG. 4A;

FIG. 5A is a sectional view taken along line E—E of FIG. 1, showing astate of contact between the position regulating member and a strainplate, where the strain plate is not in deformed (or is no-load) state;

FIG. 5B shows a state (loaded) in which the strain plate of FIG. 5A isloaded and deformed;

FIG. 6A is a perspective view showing a modification of the weighingmachine according to the first embodiment;

FIG. 6B is a plan view of the weighing machine of FIG. 6A;

FIG. 7 is a plan view of another position regulating member separatefrom the position regulating member shown in FIG. 4A;

FIG. 8 is a plan view of still another position regulating memberseparate from the position regulating member shown in FIG. 4A;

FIG. 9 is a plan view of a weighing machine according to a secondembodiment of the present invention, the weighing machine being clearedof its scale plate;

FIG. 10 is a plan view of a weighing machine according to a thirdembodiment of the present invention, the weighing machine being clearedof its scale plate;

FIG. 11 is a plan view of a weighing machine according to a fourthembodiment of the present invention, the weighing machine being clearedof its scale plate;

FIG. 12 is a plan view of a weighing machine according to a fifthembodiment of the present invention, the weighing machine being clearedof its scale plate;

FIG. 13 is an exploded perspective view showing a configuration of aconventional weighing machine; and

FIG. 14 is a plan view showing a conventional bonding method for astrain plate and a base plate member.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will be described withreference to FIGS. 1 to 8.

As shown in FIGS. 1 to 3, a weighing machine 1 comprises a strain plate4, a base plate member 3 on which the strain plate 4 is placed withoutusing fixing means such as screws or bolts, and a scale plate member 2that is located on the upper surface of the strain plate 4 and serves totransmit load to the strain plate 4.

The strain plate 4 is formed of one plate member having a substantiallyrectangular flat surface. Load receiving portions 5, which are in theshape of a hemisphere each, are fixed individually to regions near thefour corners of the upper surface of the strain plate 4. On the otherhand, receiving members 2 a in the form of a plate are fixedindividually to the portions of the lower surface of the scale platemember 2 at the portion facing the load receiving portions 5. Load thatis applied to the scale plate member 2 is transmitted to the four loadreceiving portions 5 of the strain plate 4 through the receiving members2 a.

Further, the strain plate 4 is formed with grooves that extend straightin its transverse direction (direction perpendicular to line B—B ofFIG. 1) in its central portion and form a strain-direction regulatingportion 7. Although the grooves of the strain-direction regulatingportion 7 are formed individually on the upper and lower surfaces of thestrain plate 4, as shown in FIG. 2, one of them may alternatively beformed only on the upper surface of the strain plate 4. The grooves(strain-direction regulating portion 7) formed on the strain plate 4serve to regulate the strain direction of the strain plate 4 to itslongitudinal direction (direction B—B of FIG. 1).

A strain gauge 6 is mounted on the strain plate 4 so as to extend alongline B—B of FIG. 1 astride the grooves of the strain-directionregulating portion 7. The strain gauge 6 is attached to only the uppersurface of the strain plate 4 or each of the upper and lower surfaces.The strain gauge 6 senses strain of the strain plate 4 whose straindirection is regulated. The central portion of the strain plate 4 wherethe strain-direction regulating portion 7 is excluded constitute loadtransmission beams 8 that transmit load on the load receiving portions 5to the strain gauge 6.

The four load receiving portions 5 on the strain plate are arranged soas to be symmetrical with respect to the centerline of each groove ofthe strain-direction regulating portion 7 and also line B—B of FIG. 1.

Base plate balls 19, which are in the shape of a hemisphere each, arefixed to the lower surface of the strain plate 4 at regions near thefour corners thereof, respectively. As shown in FIG. 2, the base plateballs 19 are arranged remoter from the strain-direction regulatingportion 7 than the load receiving portions 5 are. In other words, thedistance between the base plate balls 19 in the longitudinal directionis greater than the distance between the load receiving portions 5 inthe longitudinal direction. However, the distance between the base plateballs 19 in the transverse direction is equal to the distance betweenthe load receiving portions 5 in the transverse direction.

Receiving members 11 in the shape of a plate are provided on the uppersurface of the base plate member 3 at the locations opposite the baseplate balls 19 of the strain plate 4. On the other hand, leg portions 10are provided on the lower surface of the base plate member at thelocations opposite the receiving members 11.

As described above, the strain plate 4 is supported on the receivingmembers 11 of the base plate member 3 by means of the base plate balls19 that are arranged remoter from the strain-direction regulatingportion 7 than the load receiving portions 5. If the scale plate member2 is loaded with an object (human body or the like) to be weighed, it isdeformed only in the direction perpendicular to the grooves of thestrain-direction regulating portion 7, that is, in the direction of lineB—B of FIG. 1. The strain gauge 6 detects strain that is attributable todeformation in a portion near the center of the strain plate 4.

An output signal from the strain gauge 6 is processed in a signalprocessing circuit (not shown), and a display portion 12 displays theload of the object to be weighed, as shown in FIG. 3. In FIG. 3, number13 denotes a power switch of the weighing machine 1.

As shown in FIG. 1, the strain plate 4 that is placed on the base platemember 3 is held so that its sides C perpendicular to the straindirection B—B are positioned with respect to the base plate member 3 bymeans of a plurality of elastic position regulating members 14. Theseposition regulating members 14 are attached to the base plate member 3.

The position regulating members 14 are substantially L-shaped blocks,which are arranged individually in regions near the four corners of thestrain plate 4, whereby regions near the end portions of the sides C ofthe strain plate 4 in the direction perpendicular to the straindirection B—B and regions near the end portions of sides D of the strainplate 4 in the direction parallel to the strain direction B—B are heldin position.

The shape of the position regulating member 14 will now be describedwith reference to the plan view of FIG. 4A and the side view of FIG. 4B.

The position regulating member 14 is formed of an L-shaped block of anABS material or the like. Protuberances 14 a that abut against sidewalls of the strain plate 4 are provided individually on two inner sidesof the L-shaped position regulating member 14. Further, the positionregulating member 14 is formed with slits 14 b having a given lengththat extend individually inward from its opposite ends, whereby elasticportions 14 c capable of elastic deformation are formed ranging form theslits 14 b to the inner sides.

Furthermore, a mounting hole 14 d is formed in a part of the positionregulating member 14. The position regulating member 14 is mounted onthe base plate member 3 by fitting a bent portion 3 a (see FIG. 1),which is formed by slitting the base plate member 3 at a region neareach of the four corners thereof and bending the resulting stripupright, into the mounting hole 14 d.

Each protuberance 14 a on the position regulating member 14substantially has the shape of a semi-cylinder or hemisphere such thatthe friction of contact with the strain plate 4 is reduced. In the casewhere the protuberance is semi-cylindrical, it may be arranged so thatthe axial direction of the cylinder is in line with the thicknessdirection of the strain plate, as shown in FIGS. 4A and 4B, or that theaxial direction of the cylinder is perpendicular to the thicknessdirection of the strain plate (not shown).

The material that constitutes the position regulating member 14 is notlimited to the ABS material, and may be any material as far as theelastic portions 14 c can resist repeated use.

The state of contact between the position regulating member 14 and thestrain plate 4 will now be described with reference to FIGS. 5A and 5B.FIG. 5A shows a state in which the strain plate 4 is not deformed withno load on the scale plate member 2. FIG. 5B shows a state in which thestrain plate 4 is deformed with load on the scale plate member 2.

When the strain plate 4 is not deformed, as shown in FIG. 5A, the sidewall on the side C of the strain plate 4 that extends at right angles tothe strain direction B—B is in contact with the protuberance 14 a of theposition regulating member 14 on a vertical line indicated by dottedline F.

When the strain plate 4 is deformed with a load W on the load receivingportion 5, as shown in FIG. 5B, however, the strain plate 4 is deformedand inclined, so that the side wall on the side C of the strain plate 4ceases to be in line with the vertical line F, and a part of the strainplate 4 presses the protuberance 14 a of the position regulating member14. If the protuberance 14 a of the position regulating member is thuspressed by the strain plate 4, a portion of the strain plate 4 thatadjoins the slit is elastically deformed and narrows the slit width ofthe slit 14 b, thereby absorbing the deformation of the strain plate 4.

If the load is removed from the state shown in FIG. 5B, the strain plate4 is restored to its original flat state by its elasticity, and the sideface C of the strain plate 4 is pressed by the protuberance 14 a of theposition regulating member 14 by the elastic force of the elasticportion 14 c of the position regulating member 14, whereupon the strainplate 4 is restored to its original position shown in FIG. 5A. Thus, thedisplacement of the strain plate 4 is absorbed by the elastic force ofthe position regulating member 14, so that no gap is formed between thestrain plate 4 and the position regulating member 14 even after repeateduse of the weighing machine 1.

Further, the position regulating member 14 also positions and holds theside D of the strain plate 4 that is parallel to the strain directionB—B as well as the side C of the strain plate 4 that extends at rightangles to the strain direction B—B. If any shock attributable to a fallor the like is applied in the direction B—B or the directionperpendicular to B—B, therefore, the position regulating member 14absorbs the displacement of the strain plate 4, so that the strain plate4 is restored to its original position. Thus, initial accuracy can bemaintained for any length of time.

Further, the strain plate 4 can be held more steadily by locating theposition regulating members 14 in regions near the four corners of thestrain plate 4. Since the friction of contact between the strain plate 4and the position regulating members 14 is minimized by means of theabutting protuberances 14 a, furthermore, the accuracy can be maintainedfor a long period of time without being substantially influenced byrepeated use, fall, etc.

The base plate member 3 is a box-shaped structure that is formed of arectangular base and side walls set up individually on the fourcircumferential sides of the base. If there are gaps between the baseplate member 3 and the position regulating members 14, as shown in FIG.1, the peripheral wall of the base plate member 3 may possibly bedeformed if the weighing machine 1 is dropped.

As shown in FIG. 6A (perspective view) and FIG. 6B (plan view),therefore, the transverse and longitudinal dimensions of the strainplate 4 with respect to the base plate member 3 are made greater than inthe case of FIG. 1 so that no gaps can be created between a peripheralwall 3 b of the base plate member 3 and the position regulating members14 shown in FIG. 4A when the position regulating members 14 are arrangednear the four corners of the strain plate 4. With this arrangement, theposition regulating members 14 can restrain the peripheral wall 3 b fromsinking inward if any external force acts on the peripheral wall 3 b ofthe base plate member 3 when the weighing machine 1 is droppedaccidentally. Alternatively, creation of the gaps between the peripheralwall 3 b of the base plate member 3 and the position regulating members14 may be prevented by making the width of each position regulatingmember 14 to be attached to the base plate member 3 greater than in thecase of FIG. 1 without changing the size of the strain plate 4 shown inFIG. 1.

By increasing the transverse and longitudinal dimensions of the strainplate 4, creation of the gaps between the peripheral wall 3 b of thebase plate member 3 and the position regulating members 14 may beprevented when the position regulating members 14 are arranged in theregions near the four corners of the strain plate 4. Alternatively, theposition regulating members 14 themselves may be sized so that no gapscan be created between the position regulating member 14 and theperipheral wall 3 b of the base plate member 3.

FIGS. 7 and 8 show position regulating members having constructionsdifferent from that of the position regulating member 14 shown in FIGS.4A and 4B.

A position regulating member 14A shown in FIG. 7 is an L-shaped blockthat is formed of an ABS material or the like. Coil springs 14 e arefixed individually to two inner sides of the L-shaped positionregulating member 14A. One end of each coil spring 14 e is fixed to theside face of the position regulating member 14A, while the other end iselastically in contact with the wall surface of the strain plate 4.Thus, the coil spring 14 e combines the respective functions of theprotuberance 14 a and the elastic portion 14 c of the positionregulating member 14 shown in FIG. 4A (and therefore, the positionregulating member 14A need not be provided with any slit for theformation of the elastic portion).

Further, the position regulating member 14A is formed with a mountinghole 14 d such that the position regulating member 14A can be fixed tothe base plate member 3 by fitting the mounting hole 14 d on the bentportion 3 a (see FIG. 1) of the base plate member 3.

These coil springs 14 e are configured to hold the side D of the strainplate 4 that is parallel to the strain direction B—B as well as the sideC of the strain plate 4 that extends at right angles to the straindirection B—B. Accordingly, the same functions as aforesaid can befulfilled, that is, the position regulating members 14 can absorb thedisplacement of the strain plate 4 if the weighing machine 1 is usedrepeatedly or any shock of a fall or the like acts on the strain plate4. After the load is removed, therefore, the strain plate 4 is restoredto its original position, so that the initial accuracy can be maintainedfor any length of time.

In a position regulating member 14B shown in FIG. 8, leaf springs 14 fare used in place of the coil springs 14 e of the position regulatingmember 14A described above. One end portion of each leaf spring 14 f ismolded in an L-shaped wall, while the other end portion is formed with aprotuberance 14 g that abuts against the side C or the side D of thestrain plate 4 extending at right angles or parallel to the straindirection B—B. Further, the position regulating member 14B is providedwith a mounting hole 14 d. Constructed in this manner, it has the samefunctions as that of the position regulating member 14A described above.

A second embodiment of the present invention will now be described withreference to FIG. 9.

In this embodiment, elastic position regulating members 15 are arrangedon sides C of a strain plate 4 that extend at right angles to its straindirection B—B, while fixing members 16 are arranged on sides D of thestrain plate 4 that are parallel to the strain direction B—B.

Each position regulating member 15 is a rectangular block that is formedof an ABS material or the like. A protuberance 15 a is provided on theside face of the position regulating member 15 which faces a side wallof the strain plate 4. Thus, the position regulating member 15 comesinto contact with a side wall C of the strain plate 4 through itsprotuberance 15 a. The position regulating member 15 is formed with aslit 15 b with a given length that extends parallel to its side face onwhich the protuberance 15 a is provided, whereby an elastic portion 15 ccapable of elastic deformation is formed adjacent to the slit 15 b.

Further, a mounting hole 15 d is formed in the position regulatingmember 15, and the position regulating member 15 can be fixed to a baseplate member 3 by fitting the mounting hole 15 d on a bent portion 3 aof the base plate member 3.

Each fixing member 16 is a rectangular block that is formed of an ABSmaterial or the like. A protuberance 16 a is provided on the side faceof the fixing member 16 which engages a side wall D of the strain plate4. Thus, the fixing member 16 comes into contact with the side D of thestrain plate 4 through its protuberance 16 a. Further, the fixing member16 is provided with a mounting hole 16 b such that the fixing member 16can be fixed to the base plate member 3 with the mounting hole 16 bfitted on the bent portion 3 a of the base plate member 3.

Preferably, four position regulating members 15 in total should bearranged opposite the sides C of the strain plate 4 perpendicular to thestrain direction B—B and in positions at equal distances from line B—B.The position of the strain plate 4 can be kept particularly stable ifthe position regulating members 15 are arranged near the opposite endportions of the sides C of the strain plate 4. Further, four fixingmembers 16 in total should be arranged near the four end portions of thesides D of the strain plate 4 parallel to the strain direction B—B suchthat they oppose the sides D.

If a load is applied to a weighing machine 1 shown in FIG. 9, the strainplate 4 is deformed to press the protuberances 15 a of the positionregulating members 15. Thereupon, the portions adjacent to the slits 15b of the position regulating members 15 are elastically deformed tonarrow the slit width, thereby absorbing the deformation of the strainplate 4. As this is done, the protuberances 16 a of the fixing members16 are in contact with the side faces D of the strain plate 4 andprevent the strain plate 4 from being dislocated. When the load isremoved from the weighing machine 1, the strain plate 4 is restored toits original position by the elastic force of the elastic portions 15 dof the position regulating members 15.

In the weighing machine 1 shown in FIG. 9, the displacement of the sidesC of the strain plate 4 perpendicular to the strain direction B—B, whichis attributable to the deformation of the strain plate 4, is absorbed bythe elastic position regulating members 15, and the fixing members 16engage and hold the sides D of the strain plate 4 parallel to the straindirection B—B. Accordingly, dislocation of the strain plate 4 can beprevented and the position of the strain plate 4 never changes if thefrequency of use increases, so that the measurement accuracy can bemaintained for a long period of time. If the weighing machine 1 isdropped, moreover, a shock that acts in the strain direction of thestrain plate 4 can be absorbed. A shock that acts in a directionperpendicular to the strain direction of the strain plate 4 when theweighing machine is dropped can be satisfactorily absorbed in a casewhere the sides D are also positioned and held by means of the elasticposition regulating members, as will be described later in connectionwith a fourth embodiment mentioned.

A third embodiment of the present invention will now be described withreference to FIG. 10.

In this embodiment, one elastic position regulating member 17 isarranged opposite each side C of a strain plate 4 that extends at rightangles to its strain direction B—B.

The position regulating member 17 is a rectangular block that is formedof an elastic member such as a rubber material. A protuberance 17 a isprovided on the side face of the position regulating member 17 whichfaces a side wall C of the strain plate 4. Thus, the position regulatingmember 17 comes into contact with the side C of the strain plate 4through its protuberance 17 a. Further, the position regulating member17 is provided with a mounting hole 17 b. The position regulating member17 is fixed to a base plate member 3 with the mounting hole 17 b fittedon a bent portion 3 a of the base plate member 3.

Since fixing members 16 are similar to the ones (fixing members 16 shownin FIG. 9) according to the aforementioned second embodiment, and adescription of them is omitted.

In positioning and holding each side C of the strain plate 4perpendicular to the strain direction B—B by means of the one positionregulating member 17, the position regulating member 17 shouldpreferably be arranged in a position substantially opposite to thecenter of the side C, as shown in FIG. 9. Further, the fixing members 16are arranged in the same positions (positions of the fixing members 16shown in FIG. 9) as those in the case of the second embodiment.

In a weighing machine 1 shown in FIG. 10, the displacement of the sidesC of the strain plate 4 perpendicular to the strain direction B—B, whichis attributable to the deformation of the strain plate 4, is absorbed bymeans of the elastic position regulating members 17, and the fixingmembers 16 engage and hold sides D of the strain plate 4 parallel to thestrain direction B—B. Accordingly, dislocation of the strain plate 4 canbe prevented. Since the position of the strain plate 4 never changes ifthe frequency of use increases, therefore, the measurement accuracy canbe maintained.

Further, a shock that acts in the strain direction of the strain platein case of a fall or the like can be absorbed. When the load is removedfrom the weighing machine 1, the strain plate 4 is restored to itsoriginal position by the elastic force of the rubber material of theposition regulating members 17. A shock that acts in a directionperpendicular to the strain direction of the strain plate 4 in case of afall can be satisfactorily absorbed in a case where the sides D are alsopositioned and held by means of the elastic position regulating members,as will be described later in connection with the fourth embodimentmentioned.

The fourth embodiment of the present invention will now be describedwith reference to FIG. 11.

In this embodiment, a strain plate 4 is formed with openings 18 that arearranged on a line in the strain direction B—B of the strain plate 4 inpositions symmetrical with respect to the strain gauge 6. An elasticposition regulating member 17 is arranged opposite an inner wall surfaceG of each opening 18 that extends at right angles to the straindirection on the side of the strain gauge 6. Further, four elasticposition regulating members 17 in total are arranged near the endportions of the sides D of the strain plate 4 parallel to the straindirection B—B such that they oppose the sides D.

Preferably, the position regulating members 17 to be arranged in theopenings 18 should be arranged in regions where ranges in which forcepropagates when load is applied are excluded. In other words, theyshould be arranged as far from straight lines that connect loadreceiving portions 5 and the strain gauge 6 as possible.

The six position regulating members 17 shown in FIG. 11 is the same onesas those described in connection with the third embodiment (FIG. 10).Thus, individual position regulating member 17 comes into contact withthe strain plate 4 by means of its protuberance 17 a, and is fixed to abase plate member 3 with its mounting hole 17 b fitted on a bent portion3 a of the base plate member 3.

In a weighing machine 1 shown in FIG. 11, the deformation of the strainplate 4 is absorbed by the elastic position regulating members 17 thatare individually in contact with the respective inner wall surfaces G ofthe openings 18 extending at right angles to the strain direction B—B ofthe strain plate 4, and the position regulating members 17 are caused toengage the sides D of the strain plate 4 parallel to the straindirection B—B, whereby dislocation of the strain plate 4 is prevented.Since the position of the strain plate 4 never changes if the frequencyof use increases, therefore, the measurement accuracy can be maintained.

Further, a shock caused by a fall of the weighing machine 1 can beabsorbed by the six position regulating members 17. When the load isremoved from the weighing machine 1, the strain plate 4 is restored toits original position by means of the elastic force of the rubbermaterial of the position regulating members 17. Since the strain plate 4is provided with the openings 18, moreover, the strain plate 4 islightened correspondingly. Further, as the position regulating members17 are arranged inside the outer wall of the strain plate 4, theexternal shape can be reduced.

A fifth embodiment of the present invention will now be described withreference to FIG. 12.

In this embodiment, the four corners of a substantially rectangularstrain plate 4 are cut off at an angle of 45° to form four oblique sidesH1 and H2, and elastic position regulating members 17 are opposed to theoblique sides H1 and H2 of the strain plate 4, individually.

The elastic position regulating members 17 are identical with theposition regulating members that are used in the third embodiment (FIG.10) and the fourth embodiment (FIG. 11).

The position regulating members 17 are arranged opposite the sides H1and H2 of the strain plate 4 that are inclined at an angle of 45° to thestrain direction. Accordingly, the individual position regulatingmembers 17 absorb the displacement of the oblique sides H1 and H2 whichis attributable to the deformation of the strain plate 4, by theirelasticity, and prevent dislocation of the strain plate 4.

Further, a shock that is caused by a fall of a weighing machine 1 can beabsorbed by elastic deformation of the four position regulating members17.

According to the weighing machine 1 of FIG. 12, compared with fourthembodiment, the position regulating members 17 can be reduced from 6 to4 in number.

In the first to fifth embodiments of the present invention, the positionregulating members 14, 15 and 17 are provided with the protuberances 14a, 15 a and 17 a to lessen the friction of contact with the strain plate4. Alternatively, however, protuberances may be formed on the strainplate 4 without providing the position regulating members with anyprotuberances.

INDUSTRIAL APPLICABILITY

In the weighing machine according to the present invention, the strainplate is positioned and held by means of the elastic position regulatingmembers that are mounted on the base plate member, so that theelasticity of the position regulating members can absorb thedisplacement of the strain plate that is caused when the strain plate isdeformed as the weighing machine is loaded. When the strain plate isrestored to its original state after the load is removed from theweighing machine, the position regulating members follow thedisplacement of the strain plate by their elastic force. Even when theweighing machine is not loaded, therefore, the position regulatingmembers are always in contact with the strain plate, so that theposition of the strain plate relative to the base plate member thatcarries it thereon can be kept fixed.

What is claimed is:
 1. A weighing machine comprising a substantiallyflat strain plate adapted to be deformed when loaded, a sensor fordetecting deformation of said strain plate, a base plate member carryingsaid strain plate thereon, and a scale plate member located on the uppersurface of said strain plate and capable of transmitting load to saidstrain plate, wherein said strain plate is placed on said base platemember without being fixed to said base plate member, and sides of saidstrain plate are held by means of elastic position regulating members,individually.
 2. The weighing machine according to claim 1, wherein saidstrain plate has a strain-direction regulating portion for regulatingthe direction of a strain produced in said strain plate as said strainplate is deformed, said sensor is a strain gauge attached to said strainplate corresponding to the strain direction of said strain plate, andsaid position regulating members hold at least the sides of said strainplate which extend at right angles to said strain direction.
 3. Theweighing machine according to claim 2, wherein said strain plate isformed with at least two sides extending at right angles to said straindirection, opposed to each other across said strain-direction regulatingportion, and said two sides are held by said position regulatingmembers, individually.
 4. The weighing machine according to claim 3,wherein said position regulating members for holding the sidesperpendicular to said strain direction hold the sides of said strainplate perpendicular to said strain direction at a plurality of portionsthereof.
 5. The weighing machine according to claim 4, wherein saidposition regulating members for holding the sides perpendicular to saidstrain direction hold the sides of said strain plate perpendicular tosaid strain direction at two portions near the opposite end portionsthereof.
 6. The weighing machine according to claim 2, wherein saidposition regulating members hold the sides of said strain plate whichextend parallel to said strain direction as well as the sides of saidstrain plate perpendicular to the strain direction.
 7. The weighingmachine according to claim 6, wherein said strain plate is formed with aplurality of sides parallel to said strain direction, and said pluralityof sides are held by means of said position regulating members.
 8. Theweighing machine according to claim 7, wherein said position regulatingmembers for holding the sides parallel to said strain direction hold thesides of said strain plate parallel to said strain direction at portionsnear the end portions thereof.
 9. The weighing machine according toclaim 7, wherein said strain plate is formed with at least two sidesextending at right angles to said strain direction and opposed to eachother across said strain-direction regulating portion, and said positionregulating members for holding the sides perpendicular to said straindirection hold the sides perpendicular to said strain direction at oneportion near the center thereof, respectively.
 10. The weighing machineaccording to claim 1, wherein each said position regulating memberincludes a fixed portion fixed to said base plate member and a contactportion formed integrally with said fixed portion and in contact withthe side of said strain plate, and said contact portion is made elasticby a slit formed between said contact portion and said fixed portion.11. The weighing machine according to claim 1, wherein each saidposition regulating member is composed of a fixed portion fixed to saidbase plate member and an elastic portion in contact with the side ofsaid strain plate and attached to said fixed portion.
 12. The weighingmachine according to claim 2, wherein said strain plate has two openingsin positions symmetrical with respect to the strain gauge, and saidposition regulating members hold the inner walls formed in saidopenings.
 13. The weighing machine according to claim 1, wherein eachsaid position regulating member has a protuberance, and saidprotuberance is in contact with the side of said strain plate.
 14. Theweighing machine according to claim 1, wherein the individual sides ofsaid strain plate are arranged so as to be in contact with said positionregulating members only.
 15. The weighing machine according to claim 6,wherein the plane shape of said strain plate is substantiallyrectangular, and said position regulating members are substantiallyL-shaped members arranged individually near the four corners of saidrectangular shape.
 16. The weighing machine according to claim 15,wherein said substantially L-shaped member is formed with a hole portionsuch that the L-shaped member can be fixed to said base plate memberwith said hole portion fitted on a fitting member protrudingsubstantially perpendicularly from said base plate member.
 17. Theweighing machine according to claim 6, wherein said position regulatingmembers for holding the sides of said strain plate perpendicular to thestrain direction and said position regulating members for holding thesides of said strain plate parallel to the strain direction are formedseparately from one another.
 18. A weighing machine comprising asubstantially flat strain plate adapted to be deformed when loaded, asensor for detecting deformation of said strain plate, a base platemember carrying said strain plate thereon, and a scale plate memberlocated on the upper surface of said strain plate and capable oftransmitting load to said strain plate, wherein said strain plate isplaced on said base plate member without being fixed to said base platemember, and the position of said strain plate in the planar direction issettled by means of elastic position regulating members.
 19. Theweighing machine according to claim 15, wherein the portion of saidL-shaped member which faces a side of said strain plate perpendicular tothe strain direction is provided with a slit extending parallel to theside perpendicular to said strain direction, and the portion of saidL-shaped member which faces a side of said strain plate parallel to thestrain direction is provided with a slit extending parallel to the sideparallel to said strain direction, whereby said L-shaped member is madeelastic.
 20. The weighing machine according to claim 13, wherein saidprotuberance is in the shape of a semi-cylinder or hemisphere.
 21. Theweighing machine according to claim 16, wherein said fitting member isformed by slitting and raising a part of said base plate member.
 22. Theweighing machine according to claim 15, wherein said base plate memberhas side walls set up thereon, and the size of said position regulatingmembers is regulated such that gap be not formed between said side walland said position regulating member.
 23. The weighing machine accordingto claim 1, wherein said position regulating members are formed of anelastic material such as rubber.
 24. The weighing machine according toclaim 1, wherein said strain plate is formed with a straight groove forregulating the direction of a strain formed as said strain plate isdeformed, said strain plate has oblique sides inclined at about 45° tothe direction of said groove, and said oblique sides are held by meansof said position regulating members, individually.